Valve devices for switching the flow direction of various kinds of coolants in several paths are generally used in different industrial fields.
Particularly, vehicles are provided with a variety of valve devices. Such valve devices are configured to distribute or control the flow of different kinds of coolants that are provided depending on the purposes, such as cooling a drive source (an internal combustion engine for a vehicle or a battery for an electric vehicle), air conditioning of a passenger compartment, exhaust gas recirculation (of an EGR system), etc.
For example, a coolant control valve for cooling a drive source (an engine or a battery) is configured to control the flow of coolant for optimizing the temperature of a transmission and enhancing the output and fuel efficiency of the engine.
The operation of the coolant control valve for controlling the flow of coolant is as follows. In a cold start, coolant discharged from an engine (a drive source) is re-supplied to the engine through a bypass line (bypassing a radiator) to warm the engine, whereby the engine can be rapidly heated to an appropriate temperature. When the engine is overheated, the coolant is supplied to the radiator through a cooling line. Coolant cooled by the radiator is drawn into the engine so as to prevent the engine from overheating. Furthermore, in the cold start, some of coolant discharged from the engine may be supplied to an oil cooler so as to heat transmission oil.
Such a valve device includes: a valve housing having at least one inlet port and at least one outlet port; a valve member rotatably provided in the valve housing; and an actuator provided to rotate the valve member. The actuator includes a drive motor, and a motor gear train connected the drive motor. The drive force of the drive motor is transmitted to a rotating shaft of the valve member by the motor gear train, whereby the valve member can be rotated. The inlet port and the outlet port of the valve housing can selectively communicate with each other depending on the rotation of the valve member.
Meanwhile, the valve device has a fail-safe function in which the valve member is returned to its original position by a return spring provided on the rotating shaft of the valve member when an error of a control circuit, a failure of the drive motor or damage to the motor gear train is caused.
However, the conventional valve device uses a large-capacity drive motor because a comparatively large amount of power is required to overcome the elastic force of the return spring. Therefore, the production cost of the valve device is increased. Moreover, it is difficult to reduce the sizes and weights of parts because the large-capacity drive motor is used.